Fish vendors at Beijing's biggest seafood market have been using a dental treatment that is believed to have a tranquilising effect to help reduce fish deaths and injuries during transport, triggering more public concerns over food safety.

Many vendors pour zinc oxide eugenol cement, which is usually used for temporary dental fillings, into tanks before delivering fish to customers, China National Radio reported on Tuesday.

Although there is no scientific evidence that the practice could harm consumers, it is not a permitted food additive.

Vendors at Beijing Dahongmen Jingshen seafood market were quoted as saying that the cement, which usually sells for 12 yuan (HK$15) per 200 millilitre pack, helps to calm fish during the travelling, reducing the chance of injury from jumping and reducing death rates by at least 10 per cent.

Tong Yanjian, who mainly trades lobsters at the market, said that tranquilising fish during transport had been a common practice in the industry for years.

'Usually people add some tranquiliser to the water before transporting fish. This way the fish becomes quiet and won't hurt itself from jumping. When it arrives at the market, it revives and looks good,' he said.

He said that people used to use machines to add oxygen to the water during transport to prevent fish from dying, but adding chemicals was cheaper.

He said that tranquilised fish were safe to eat as long as they recovered after being transported.

Dentist Chen Yadong said that zinc oxide eugenol cement was typically used to temporarily fill a hole during treatment of tooth decay. 'The eugenol in this product may have some tranquilising effect,' he said, adding that there was no proof that it was harmful to humans.

There are no regulations governing the use of tranquilisers while transporting fish on the mainland. While zinc oxide eugenol cement is not on the government's list of permitted food additives, which means it's banned in food, fishery industry regulations do not explicitly ban the use of tranquilisers during transport.

A report by the European Inland Fisheries Advisory Commission, based on research carried out as early as 1983 and 1984, said that many chemicals are commonly used as anaesthetics when transporting fish, but eugenol is not among those mentioned.

The European report also said it was illegal to use anaesthetics if the fish would be consumed soon after exposure.

$10.6b

The value, in US dollars, or 2.97 million tonnes, of fishery products exported from the mainland, according to 2008 figures